This invention relates to a single-lens reflex camera, and more specifically to a single-lens reflex camera provided with a mirror driving mechanism for swinging a movable mirror having a focusing detection mirror used for a focusing detecting device.
In a prior art focusing detecting device, a detection mirror is fixed on a movable mirror at right angles to the back of the movable mirror so that part of light transmitted through a camera lens may be led to the detection mirror through a light transmitting or half-transmitting section of the movable mirror. Accordingly, when the movable mirror is moved off the optical path of the camera lens, inverse incident light from a finder eyepiece section will be undesirably transmitted through the light transmitting or half-transmitting section of the movable mirror. Use of shielding means for intercepting the inverse incident light will, however, complicate the construction of the device. When the movable mirror is moved out of the optical path, moreover, the detection mirror fixed on the back of the movable mirror will inevitably be put in the optical path. In order to eliminate such drawbacks, there is proposed a driving mechanism to drive the detection mirror in a folding manner, interlocking with the movement of the movable mirror. As an example of such mechanism, there is a reflector driving system for a single-lens reflex camera with a built-in exposure meter disclosed in Japanese Patent Publication No. 51253/72.
In this mechanism, a detection mirror is swingably mounted on the back of a movable mirror, and a pin attached to one end of an extended section on the back of the detection mirror is guided by a guide groove formed in an extended section on the back of the movable mirror. A spring is interposed between these two mirrors. The two mirrors are so biased as to be separated from each other by the spring. As a result, the detection mirror is removed from the movable mirror until the pin abuts against one end of the guide groove, thereby opening an aperture of the movable mirror. The movable mirror is swingably mounted on the base plate of the camera body by means of a guide arm swingably mounted on the base plate. On the other hand, one end of a driving lever with the other end rotatably mounted on the base plate is pivotally mounted on the extended section of the movable mirror. The movable mirror is swung when the driving lever is continuously driven to swing by a shutter. Further, the driving lever has a pin fixed thereon at a portion a little ahead of the other end portion of the extended section of the detection mirror. As the driving lever swings, this pin engages the other end portion of the extended section of the detection mirror, and causes the detection mirror to swing to the movable mirror side against the biasing force of the spring.
The mechanism of such conventional type, however, requires a number of parts or components which complicates the construction, undesirably leading to a reduction in detection accuracy.